Touch screens can be divided into various types, such as resistive type, capacitive type, surface infrared type, acoustic wave type and the like. A touch display may be formed by attaching one layer of special metallic conductive material (touch-sensitive layer) on a surface of a glass. When a finger touches on the metallic layer, a capacity on the touching point changes, which makes a frequency of an oscillator connected to the metallic layer change. Information on the touch position may be obtained by measuring change of the frequency. In a capacitive touch screen of on cell type which is produced on the basis of a Liquid Crystal Display (LCD), a grounded shielding circuit layer of Indium Tin Oxide (ITO) will be disposed between a touch-sensitive layer and a display device. When an electrical signal is introduced to the touch-sensitive layer (TP sensor) part, the touch-sensitive layer will form a coupled capacity with the ITO shielding circuit layer and produce a phenomenon of charge-discharge, so that a capacity of the touch-sensitive layer is influenced and an abnormal operation is caused.